The present invention relates to a picture display using CMOS (Complementary Metal Oxide Semiconductor) image sensor; and, more particularly, to a CMOS image sensor having a testing circuit embedded therein and a method for verifying operation of the CMOS image sensor using the testing circuit.
Generally, an image sensor is an apparatus to capture images using light sensing semiconductor materials. Since brightness and wavelength of light from an object has different amounts according to the reflection area, electrical signals from pixels are different from one another. These electrical signals are converted into digital signals, which can be processed in a digital circuit, by an analogue-to-digital converter.
Conventional displays employing charge coupled devices (hereinafter, referred to as CCDs) are in need of relatively high voltage and many processing steps are required to implement such a charge coupled device. An image sensor implemented by the charge coupled devices should have separate logic circuits for converting the analogue signals into the digital signals. Furthermore, in the conventional CCD image sensor, it is very difficult to integrate the sensors and the logic circuits in a chip.
It is, therefore, an object of the present invention to provide a CMOS image sensor capable of being driven in a low power using a CMOS technology.
It is another object of the present invention to provide a CMOS image sensor in which sensors and all logic circuits are integrated in a chip with a fast data processing and a large integration.
It is further another object of the present invention to provide a CMOS image sensor with a test logic circuit for verifying its operation and a method for verifying the CMOS image sensor.
In accordance with an aspect of the present invention, there is provided a CMOS image sensor comprising: a control and interface means for controlling the CMOS image sensor using a state machine and for interfacing the CMOS image sensor with an external system; a pixel array including a plurality of pixels sensing images from an object and generating analogue signals according to an amount of incident light; a conversion means for converting the analogue signals into digital signals to be processed in a digital logic circuit; and a logic circuit for testing operations of the conversion means and the control and interface means, by controlling the conversion means.
In accordance with another aspect of the present invention, there is provided a CMOS image sensor having a pixel array to output analogue signals sensed from an object, the CMOS image sensor comprising: an analogue-to-digital converter including: a) a voltage generator for generating a first reference voltage; b) a comparison means for comparing the analogue signals with the reference voltage; and c) a storage means for storing digital signals in response to outputs from the comparison means; and a logic circuit for detecting whether the analogue-to-digital converter operates erroneously or not, wherein the logic circuit operates in response to test mode information stored in a mode register which the CMOS image sensor has, controls the voltage generator for the comparison means to receive a second reference to voltage and a test voltage and stores in the storage means digital signals produced in response to a control signal from the comparison means, and wherein the storage means outputs the stored digital signals to an output terminal of the CMOS image sensor.